Manufacture of molded composition friction bodies



Dec. 4, 1945. E. E NOVOTNY MANUFACTURE OF MOLDED COMPOSITION FRICTIONBODIES 3 Sheets-Sheet 1 Original Filed July 2, 1945 INVENTOR.

ATTORNEY.

' Dec. 4, 1945. E. E. NOVOTNY 2,390,266

MANUFACTURE OF MOLDED COMPOSITION FRICTION BODIES Original Filed July 2,1943 3 Sheets-Sheet 2 INVENTOR.

ATTORNEY.

Emil E. [Va/05mg lll Dec. 4, 1945. E NOVOTNY 2,390,266

MANUFACTURE OF MOLDED COMPOSITION FRICTION BODIES Original Filed July 2,1943 5 Sheets-Sheet 3 INVENTOR.

Ema! ETA/0002929 M ATTORNEY.

Patented Dec. 4; 1945 MANUFACTURE OF MOLDED COMPOSITION FRICTION BODIESEmil E. Novotny, Prospectville, Pa., asslgnor to Durlte Plastics,Incorporated, Philadelphia, Pa., a corporation of Pennsylvania Originalapplication July 2, 1943, Serial No.

Divided and this application August 21, 1943, Serial No. 499,469

11 Claims.

This invention relates to the manufacture of molded composition frictionor tractive-surface bodies such as brake linings, brake blocks, clutchfacings, etc.-

Friction or tractlve-surface articles have been made by a number ofmethods including that involving the mixing of a heat-reactable binderwith asbestos fibres, with or without fillers, and then molding the sameunder heat and pressure to the desired shape. A common form of binderfor this purpose is a potentially reactive synthetic resin. In makingsuch friction bodies, relatively long-fibred asbestos and a potentiallyreactive synthetic resin are carefully mixed. It is generally desirableto use a minimum amount of binder and a maximum amount of asbestosfibres and fillers, the proportion of the latter to the resin binderbeing usually about ten to one. The very form and shape of the fiuflyasbestos fibres, particularly in the relatively high amounts used, makesit difllcult to uniformly distribute the binder resin throughout themass. If the binder is not uniformly distributed, then the resultantfriction article will vary in hardness or density, the frictionalproperties of the material will be erratic, the wear in service will beimpaired and the difiiculties in manufacture will be increased. Toobtain a, proper moldable mix, and a resultant product of uniformhardness or density, is very difiicult through prior or present methodsof molding, even though the molding composition is carefully weighed outin small quantities, section for section, of friction stock material.

If in these prior methods of molding friction articles, 9, liquidpotentially reactive synthetic resin such as a phenol-aldehyde resin isused in the limited amounts possible, then an intimate uniform mixtureis difilcult to secure, since the liquid resins in general arerelatively quite viscous, and the volume of the resin is small comparedto the mass of fluffy asbestos fibres to be wetted and covered. If asolvent is used to increase the volume and decrease the resin viscosity,then an undesirable additional operation is required to remove thesolvent. In either case, during the heat reaction process, whenever aliquid resin is employed there is an excessive evolution of gases andwater vapor which tend to make the friction material blistered orlaminated. If dry potentially reactive synthetic resins are employed,then it is increasingly diificult to secure an intimate mixture and touniformly wet the asbestos fibres with the binding resin. Since there ismuch less evolution of gases during ouring with the use of dry resins,these are preferred in practice but these have to be employed withselected types of fiuxes or plasticizers which in themselves aretroublesome.

The prime object of my present invention centers about the provision ofa method of making molded friction or tractive-surface bodies employinga resin as a bond, in which an initial or only fairly intimate'mixtureof asbestos fibres and dry resin binder is heated andmolded underconditions of minimum pressure and in such a way that the asbestosfibres become uniformly wetted with the binding resin and become therebyalso more intimately and thoroughly intermixed to produce a homogeneousmass which is uniformly compressed into the desired molded friction bodyof uniform hardness or density.

In accordance with the principles of my present invention, an initialmix of asbestos fibres 20 and binder is heated in an enclosed heatinchamber of relatively large area and volume under low pressure, thepressure being generated in and derived from a material feed andpressure channel in open communication with the heat- 26 ing chamber,the heating chamber leading to and 30 with little or no back ressure,and there the dry resin fuses or melts, fiowing and uniformly wettingthe long asbestos fibres, becoming also thereby more thoroughlyintermixed therewith, the thus thoroughly intermixing mass beinguniformly compressed by the low operating pressure into a homogeneousstate as the mass moves through the heating chamber and is fed into themold cavity or is fed through orifices and drawn therefrom, to formproducts of the desired density, finish and form.

A further object 01' my present invention centers about the provision ofa method of making molded friction or tractive-surface bodies abovereferred to, in which the heating chamber of the desired large area andvolume consists of an electrostatic field of relatively large area andvolume defined by spaced electrodes of correspondingly large area and inwhich the mix is flowed through said field under the developedrelatively low pressure to produce the homogeneous fibre-resinimpregnated friction body.

A further object of the invention resides in the provision of a methodof this character in which the heating in the heating chamber orelectrostatic field may be sufiiciently high in temperature forexothermic reaction to take place, and for the material to cure rapidlyeven though the mold cavity be unheated, whereby, if desired, the moldedpiece may be rapidly ejected from or through the mold cavity to permitfinal reaction to take place outside the mold.

In the practice of this part of the method, sumcient heat is supplied inthe heating space, that is, the heating chamber or the electrostaticfield, for rapidly filling the mold space or mold cavity and forthermosetting the friction body (the resin bond) without the use offurther applied heat.

From one aspect of the invention, the method provides a low friction,nozzleless process of molding a fibre-resin impregnated mixture or mass.This is to be contradistinguished from the prior use in election methodsof high pressures in ejection molding used in apparatus employing smallnozzle openings. By my present improved method, the us of nozzleorifices is eliminated and there is provided large heating areas and anadjustable heating chamber with the fibre-resin mixfiowing through insubstantial thickness, permitting heating and molding operations to becarried out at relatively low pressures. My present invention is also tobe contradistinguished from prior transfer or injection molding methodsin which the pisstic material is preheated, the mold cavity must beheated and a multiplicity of relatively small orifices are provided inthe molding apparatus. By the method of my present invention, thepreheating of the material is obviated, the orifices or nozzles efl'ecteliminated, and there is permitted the molding of a fibre-resin mixwhich has been highly plasticized at high temperature, and which Figurel is a partly sectioned, longitudinal cross-sectional view of theessential parts of a molding apparatus used in practicing the method,showing the position of the parts after a molding cycle and at the startof the new cycle;

Figure 2 is a partly sectioned, longitudinal cross-sectional view of theapparatus showing the position of the parts when the mold cavities havebeen filled; and

Figure 3 is a partly sectioned, longitudinal cross-sectioned view of theapparatus showing the position of the parts when the molded parts arebeing elected after completion of the molding cycle but with theelements of the heating space remaining closed.

The method of my present invention may be described by reference to thecorelated parts of the apparatus depicted in the drawings. An initial oronly fairly intimate mixture of asbestos fibres and dry resin flows froma pressure chan-' nel L through a heating chamber P of large area andvolume defined by the units and O to one or more mold cavities U by wayof the connecting passages .W. The pressure channel L, which is both amaterial feed and pressure channel, opens directly into the heatingchamber P, and the s id heating chamber acts to heat the asbestos-resinmix therein under the low pressure generated or produced in the feed andpressure channel L. The heating chamber P=.leads to and communi- 5 cateswith the mold cavities U by way of the passages W. The units 0' and 0 inthe form of the invention here shown comprise electrodes forelectrostatically heating the asbestos-resin mix in the chamber P, theunit 0' being a grounded l0 electrode and the unit 0 being'an insulatedelectrode. The units or electrodes 0 and 0' are movable one relativelyto the other for the purposes referred to, the unit or electrode 0 inthe form of the invention depicted in the drawings being the movableunit and the unit or electrode 0' being the fixed unit. The moldcavities U are defined by the two mold members 8 having the parting lineT, one of which members is fixed and the other of which is movable; andassociated with the movable mold member there are provided the eieotorsY, one for each mold cavity. The mold cavities U may be suitably shapedto produce the desired shape of the particular friction body; the shapeillustrated may be considered useful for the making of brake blocks.

The material feed and pressure channel L is formed centrallyin acylinder K cored as at N, and the said cylinder K may be integrallyprovided with a material containing hopper II which opens into thepressure channel L. A ram or plunger 41 operates in the pressure channelL to force feed the material gravitating thereinto from the hopper 53(see Figs. 2 and 3) into the advance end 48 of the pressure channel Lthereby placing the material under pressure at this end 48, as depictedin Fig. 2 of the drawings.

The molding cycle may now be described by reference to this part of theapparatus as shown in the sequential views of the drawings,

v Fig. 1 shows these essential parts of the molding apparatus Just aftera molding cycle, the friction bodies formed in the mold cavities U andthe sprue gates formed in the passages W having been ejected. The moldis closed and the asbes tos-resin mix is being placed under pressure inthe advance end 48 of the pressure channel L and thereby in the heatingchamber P. T0 attain the desired pressure, the ram 41 is moving from theposition shown in Fig. 3 to the position 50 shown in Fig. 2 of thedrawings. The material in the pressure channel L is preferably unheated.The material seen in the heating chamber P remaining from a previouscharge is. in a partially heated condition, and is retained in thechamber P through suitable back draft arrangements 0 and breaking edges0 on the heating unit or grounded electrode 0'. Where electrostaticheating is used, this partial heating of the material in readiness forthe next mold cavity chargeis e accomplished through proper intervalcycling of a. timing switch 2' leading to the connector 2 attached tothe insulated electrode 0, the electrodes 0' and 0 being therebyconnected to an electrostatic high frequency generator or suitableenergy source indicated as 2". During the cycling step depicted in Fig.l, the volume of material in the heating chamber P'is heated to thedesired temperature, under the pressure generated in the pressurechannel L, between the extensive surfaces provided by the heating unitsor electrodes 0 and 0.

Fig. 2 of the drawings illustrates the condition where the moldingstroke of the rain or plunger 41 has been completed and the heatedmaterial has been caused to flow into the mold cavities.

The mold cavities U have been filled and are under pressure exerted bythe material in the advance end 48 of the pressure channel L, During theflow of the asbestos-resin mix into the mold, it is heated in transit inthe heating chamber P. The cycling may be such that the material withinthe mold cavity passages W and the cavities U has been heated to a pointof exothermic reaction, such that the molded parts in the mold cavitiesU as well as the gates within the passages W are ready for election fromthe mold. The ram 41 is also now in a position for a retracting stroketo take place.

Fig. 3 of the drawings shows the arrangement of the parts after themolding cycle has been completed. Here the friction bodies are beingelected from the mold cavities U by means of the electors Y. In thisillustration the electrode is held in closed position with the materialin the heating chamber P being heated. While the mold sections S, S areopen, the heating cycle is so arranged as to bring the material in theheating chamber P up to a maximum temperature prior to its next chargedflow to the mold cavities U. The ram 41 has been retracted to permit theentrance and feeding of fresh material from the hopper 53 into thechannel L for the next pressure charge.

The heating chamber P may, if desired, also be opened together with theopening of the mold sections S, S, as will be explained hereinafter. Inthis case, the chamber P is opened either for the purpose of adjustmentof the unit or electrode 0*, or inspection of the parts, or cleaning ofthe heating chamber and pressure channel. Ordinarily, opening of theheating chamber is not required. When opened, all of the material withinthe pressure channel L and the material adhering to the surfaces of theheating units 0' and 0 may be removed and the channels completelycleaned.

While the advantages of electrostatic high frequency heating areparticularly advantageous to my invention, it is to be understood thatthe electrodes 0' and 0 may merely be heating surfaces. providing anenclosed heating chamber P for the material feeding under pressure tothe mold, and that any suitable means of heating may be utilized.Advantages accrue from this method and construction due to the largearea and volume exposed to beating, the elimination of nozzles and theutilization of substantially lower effective molding pressures, due toreduction of frictional losses.

While this method covers the molding of articles by injection, implyinga closed mold cavity, it will be understood that this method may beutilized for molding by ejection where substantially continuous lengthsof material having uniform cross-sectional shapes are to be molded.While the molds S, S may be unheated, it will be understood that theprocess broadly covers the molding of many types of materials and thattherefore the heating or cooling of the molds is not precluded.

The apparatus may be utilized in any position. For some work calling fora large number of inserts a vertical arrangement with inserts maintainedin the mold through gravity may be advantageous. Similarly, the drawingsindicate the usual type of pressure cylinder plunger or ram. However,the exertion of pressure on the unplasticized mass and at relatively lowoperating pressures makes possible the use of a single or double screwpressure feed device, or a relatively stroke, eccentric or otherwiseoperated vibrating pressure means may be used. The construction in itssalient parts may be used in the form of the usual hydraulic pressassembly, or may even facings and the like. The initial mix of asbestosshort 7 fibres and resin binders enters the heating cham-' ber at a lowpressure, with little or no back pres-- sure, and there the dry resinfuses or melts, flowing and uniformly wetting the long asbestos fibres,becoming also thereby more thoroughly intermixed therewith, and the thusthoroughly intermixing mass is uniformly compressed by the low operatingpressure into a' homogeneous state as the mass moves through the heatingchamber and is fed into the mold cavity or into the mold space.

Referring now more in detail to the apparatus, the parts alreadydescribed may be constructed and organized to carry out the referred tofunctions and other desired operations to be described below.

The electrodes 0 and O are cored at 8 and 1, respectively, for thecirculation of a fluid heating or cooling medium. A non-electricallyconducting heating medium is utilized, which is flowed through the pipesor lines 3 and 4 connected to the insulated electrode 0 and through theinlet and. outlet pipes 5 and 5 connected to the grounded electrode 0.The heating or cooling of the cored pressure cylinder K may optionallybe carried out by a separate means, as through the coringN; and likewisethe mold S, S may be heated or cooled, as the particular requirements ofthe particular mix being molded call for, as at Z. The stationary partof section S of the mold is made conductively integral with theelectrode 0' and the cylinder K through the use of the assembly studsand nuts R so that the grounding of such mold section S or cylinder Kalso grounds the electrode 0'. The heating and/or cooling of thecylinder K and the mold S, S may optionally be handled separately andthis is true of the electrodes 0 and O to the extent that the use ofhigh frequency electrostatic heating may even be eliminated for certaintypes of molding and the heating may be carried on by any suitable fluidor liquid. In this case also the arrangement may be such that the coringor heating openings 1 and 8 provide heating surfaces having mostexcellent conductive heat transfer efficiency and may therefore bealternately heated and cooled should the cycle of operations or the typeof material call for this in order to permit molding efficiency or toprevent the setting up of the material within the heating passages orwithin the heating channel P. At 45 is indicated a straight conicaljoint between electrode 0 and the retractable mold assembly, and at 46is shown a bronze orother non-abrasive metal sleeve for taking;up. -weararranged to provide wide variations.

positive electrode remains stationary.

Variations in plasticity and melting points of plastic materials, thespeed of molding cycle, the size of the mold cavities U and otherreasons to be reviewed presently often call for variation in the volumeof material required to be delivered from heating channel P andtherefore this channel is made adjustable. This may be done by thearangemerit of the threaded coupling 43 having an insulation filling 44,the,f said filling being rotatable (threadedly) on the electrodeconnected pipe 3, and the said coupling being rotatable (threadedly) onthe internally threaded holder 42. By this or other equivalent means itis possible toadjust the cross-sectional thickness of the materialwithin channel P of the heating chamber formed between electrodes 0' and0 The insulation filling 44 as well as the insulation bushing I form themeans for insulatably supporting the electrode 0 The shape and form ofelectrodes 0' and O are also so designed as to permit the utmost inflexibility. These electrodes define a heating chamber or space of largearea and volume and which area and volume increase in the direction offlow of the mix material. In this instance the heating chamber formed byelectrode 0 is in the form of a truncated cone with a complementarynegative contour forming electrode 0'. Many materials vary in insulationresistance and many of these products, even the phenolics, are indeedpoor when heated to a high temperature so far as insulation resistanceis concerned. Furthermore, it is desirable when utilizing high frequencyelectrostatic heating to be enabled to utilize a relatively high voltageand low frequency in order to heat throughout the mass, inasmuch asextremely high frequencies may under certain conditions provide onlymore or less surface heating. For these reasons the adjustment of theheating channel P should be Where these electrodes-as indicated here,would have a surface area or approximately 14 sq. in, and the heatingchannel P would have a thickness ordinarily of approximately A; inch, itwill be found that where electrostatic heating is carried out withphenolic materials the thickness in passage P should be closer to to 1inch cross-section, particularly where the mold cavities require a largevolume of material and the heating cycle is to be efficiently rapid. Itis essential for greatest-per diem production to so balance the time ofheating, the cross section and volume to be heated against a safeoptimum heating temperature in order to provide greatest uniformity inmolding.

The apparatus provided allows the mold cavity to be opened withoutopening the heating chamber passage P. This opening of the mold cavitymay be carried out by standard or conventional apparatus but isillustrated as being carried out by means of a movable ram 25, actuatingplate 26, and connecting rods 21 which latter are attached to themovable section of the mold S. The rods 21 reciprocate in the bronzebushings 50, 5 0 provided in the stationary supporting plate 28. Theline of separation between the movable mold section S and electrode 0 isthe conical joint 45. Reciprocation of the ram 25 opens and closes themold S. S. When the mold is opened, the ejectors Y being anchoredagainst the stationary plates 29 act to eject the molded pieces.

caused by the retraction of the mold when the For opening the heatingchamber P, I provide mechanism which comprises essentially a slidingcoupling 29 connected to the holder 42 and selectively connectable tothe ram 25. The sliding coupling 29 is slidable in the bronze bushing 5|provided in the supporting plate 29. The con pling 29 has a bayonet slot32 in which pin 3| may ride freely back and forth. Pin 3| is at-- tachedto shaft 39 which in turn is attached to the actuating plate 26. Lugs 39attached to coupling 29, together with set screws 40, maintain thepredetermined static position of electrode 0". A handle 33 carrying apivoted trigger 34 rises from and is fixed to the coupling 29. Thetrigger 34 seats in either the slot 39 or the slot 49 in the peripheryof the actuating plate 26. When the handle trigger 34, against theaction of spring 35, is released from slot 36 and the handle 33 is drawndown to the point where handle trigger seats in slot 49, pin 3| iscaused to enter the bayonet slot 32, engaging the coupling 29 with theshaft 30, causing lugs 39 to enter slots or orifices H in the plate 28;and electrode 0 thus becomes free to retract with the mold cavity.Attached to coupling 29 is flange 31, provided with set screws 38, whichserve to maintain the closed position of electrode O as shown in Fig. 1.

In Fig. 3, the ram 41 is shown retracted permitting additional materialto enter the pressure channel L from'hopper 53. After that, underordinary conditions, the plastic material is in a relatively unheatedcondition in the channel L. Such material may remain in the channel Lfor an unlimited length of time, and therefore the adjustment ofmaterial fed into cavity L need be only suflicient to take care of'themold ing capacity and a surplus of material will do no harm since therewill be no danger of the product prematurely setting up within materialcavity L. The material is preferably unheated in channel L.

My method does not necessaril call for the use of electrostatic highfrequency heating, the

the material between the electrodes, the accurate timing of the cyclingof the electrostatic heating to maintain temperatures within safemaximums and minimums, and the heating of a substantial thickness andquantity of material between the electrodes, with such materialremaining in the heating chamber for a sufficient length of time toattain maximum temperatures and therefore a velocity of material withinthe heating chamber substantially lower than what would be possible if anozzle were used.

Distinguished from injection methods employing the usual highpressure,-high velocity, small cross-sectional heat transfersuperheating nozzle, the heating of the asbestos-resin mix following outthe principles of the present invention is carried out in large volumethrough the use of heating surfaces of large area, variable as tocrosssectional thickness of material to be heated, and

providing at low pressures a heated, thoroughly resin impregnated andhomogeneous mass of required volume. In the method of the presentinvention the mix is flowed from the heating chamber at substantiallyits region of greatest area and volume, such region being in directcommunication with the mold space or passage whereby the mix flows fromsaid. region directly into the mold space or passage.

The apparatus used in the present invention, when employed with highfrequency heating, provides a relatively large electrode surface and aneasily adjusted variable distance between the electrodes, thuspermitting the heating of a relativel large and thick mass or mix ofmaterial to optimum molding temperatures while maintaining a closedheating chamber during the flow of material from the heating chamber tothe mold cavity.

The method of making molded composition friction or tractive-surfacebodies embodying the principles of my present invention and the numerousadvantages flowing therefrom will, in the main, be fully apparent fromthe above detailed description thereof. It will be further apparent thatmany modifications and changes may be made -.in the method withoutdeparting from the spirit of the invention defined in the followingclaims.

I claim:

1. The method of making molded composition friction or tractive-surfacebodies which consists in mixing asbestos fibres with a thermosettingresin, in delivering the mix under a relatively low pressure into aheating chamber of large area. and volume and which area and volumeincrease in the direction of flow of the mix material, in flowing saidmix through said chamber under said relatively low pressure, and into amold space, heating said mix while in transit in said chamber, theheating of the mix in said chamber functioning to form therein ahomogeneous fibre-resin impregnated friction body brought to a moldablecondition, and flowing said mix from said chamber at substantially itsregion of greatest area and volume into said mold space, said region ofthe chamber of greatest area and volume being in direct communicationwith the mold space whereby the mix flows from said region directly inthe mold space.

2. The method of making molded composition friction or tractive-surfacebodies which consists in mixing asbestos fibres with a thermosettingresin, in delivering the mix in an unheated state and under a relativelylow pressure into a heating space defined by two spaced surfaces oflarge area which area increases in the direction of flow of the mixmaterial, in flowing said mix through said heating space under saidrelatively low pressure, and into a mold space, heating said mix whilein transit through said heating space to a moldable condition, theheating of the mix in said heating space functioning to form therein ahomogeneous fibre-resin impregnated friction body brought to themoldable condition, and flowing said mix from said heating space atsubstantially its region of greatest area into said mold space, saidregion of greatest area being in direct communication with said moldspace whereby the mix flows from said region directl into said moldspace.

3. The method of claim 1 in which sufiicient heat is supplied in theheating chamber for thermosetting the resin-without further appliedheat.

4. The method of claim 2 in which sufiicient heat is supplied in theheating space for rapidly filling the mold space and for thermosettingthe friction body without further applied heat.

5. The method of making molded composition friction or tractive-surfacebodies which consists in mixing asbestos fibres with a thermosettingresin, in delivering the mix under a relatively low pressure through anelectrostatic field of relatively large area and volume which area andvolume increase in the direction of fiow of the mix material, in flowingsaid mix through said field under said relatively low pressure, andthence into a mold space, heating said mix while in transit through saidfield, the heating of the mix functioning to form within saidelectrostatic field a homogeneous fibre-resin impregnated friction bodybrought to a moldable condition,

and flowing said mix from said field at substantially its region ofgreatest area and volume into said mold space, said region of said fieldof greatest area and volume being in direct communication with said moldspace whereby the mix flows from said region directly into said moldspace.

6. The method of claim 5 in which sufficient heat is supplied in saidelectrostatic field to rapidly fill the mold space and to thermoset thefriction body without further applied heat.

'7. The method of claim 5 in which the heat is generated in theelectrostatic field by a high frequency circuit.

8. The method of making molded composition friction or tractive-surfacebodies which consists in mixing asbestos fibres with a thermosettingresin, in delivering the mix under a relatively low pressure to anelectrostatic field defined by spaced electrodes of relatively largearea which area increases in the direction of flow of the mix material,in flowing said mix through said field under said relatively lowpressure, and thence into a mold passage, heating said mix while intransit through said field, the heating of the mix functioning to formin said field a homogeneous fibre-resin impregnated friction bodybrought to a moldable condition, and flowing said mix from said field atsubstantially its region of greatest area into said mold passage, saidregion of said field of greatest area being in direct communication withsaid mold passage whereby the mix flows from said region into said moldpassage.

9. The method of claim 8 in which a heat control fluid is flowed throughsaid electrodes.

10. The method of claim 8 in which the mix is delivered to said field ina relatively unheated and unplasticized state.

11. In the method of claim 8 the added step of adjusting theelectrostatic field and heating space by adjusting the spacing betweenthe electrodes.

EMIL E. NOVOTNY.

